The present invention relates to a microwave-assisted magnetic recording and reproducing apparatus provided with a microwave power generator and a thin film magnetic head including a microwave transmission line.
It is desired to increase a recording density of a magnetic recording medium, which is a magnetic recording device. In order to keep a signal quality (an S/N ratio) necessary for high-density recording, as a areal recording density is increased, it is necessary to make magnetic particles be smaller that constitute a magnetic recording medium. However, magnetic particles that have been made smaller tend to lose magnetization because of thermal fluctuations. In order to prevent this and keep a stable recording state, it is necessary to increase magnetic anisotropy energy (Ku) of magnetic particles. The strength of a magnetic field to reverse the magnetization of magnetic particles having uniaxial magnetic anisotropy is called an anisotropic magnetic field (Hk), which is expressed using saturation magnetization (Ms) and magnetic anisotropy energy (Ku) as Hk=2Ku/Ms. Thus, in the case where a material having a high Ku is used, Hk is increased and a higher recording magnetic field is necessary to perform recording on a magnetic recording medium. In contrast, as an areal recording density is increased, the size of a recording head element is reduced. Thus, the strength of a magnetic recording field that may be generated decreases proportionately with the size of a recording head element. As a result, recording to be performed on the magnetic recording medium becomes difficult.
To perform magnetization reversal of a recording film that has smaller grain and whose magnetic anisotropy energy (Ku) is high, the recording head element of a thin film magnetic head needs to apply an abrupt recording magnetic field having, at maximum, a strength of the order of the anisotropic magnetic field (Hk) of the recording film. In a magnetic disk drive (Hard Disc Drive: HDD) that has become commercially practical using a perpendicular magnetic recording method, a recording head element using a so-called monopole is used and a recording magnetic field is applied to a recording film in a perpendicular direction from a surface of an air bearing surface (Air Bearing Surface: ABS) of the recording head element. The strength of this perpendicular recording magnetic field is proportional to a saturation magnetic flux density (Bs) of a soft magnetic material that constitutes the monopole, and thus a material having a saturation magnetic flux density (Bs) that is made as high as possible has been developed and has become commercially practical. However, as a saturation magnetic flux density (Bs), Bs=2.4 T (tesla) is practically the upper limit from a so-called Slater-Pauling curve, and a value obtained under present circumstances is approaching the practical limit. In addition, the thickness and width of a monopole currently used is on the order of about 100 nm to 200 nm; however, in the case where a recording density is increased, it is necessary to further reduce the thickness and width. As a result, a perpendicular magnetic field to be generated is further reduced.
In this manner, under present circumstances, it is becoming more difficult to achieve higher density recording because of the limit of the recording capability of a recording head element. In order to solve this technical problem, energy assisted recording has been proposed in which, when recording is performed, energy is applied to a magnetic recording medium in an auxiliary manner and a magnetic field strength necessary for signal recording is reduced.
A recording method using a microwave magnetic field as an auxiliary energy source is called a microwave assisted magnetic recording (Microwave Assisted Magnetic Recording: MAMR). (Non-Patent Literature 1)